Aircraft multi-axis modal suppression system

ABSTRACT

Vibrations due to excitation of the natural modes of an aircraft&#39;s body are suppressed by an active multi-axis modal suppression system. Dedicated sensors are positioned in the aircraft at optimal locations for sensing modal induced vibrations. The sensor produced signals are processed through control logic which, in response thereto, and in response to aircraft inertial, velocity and altitude related signals produces output control signals. The control signals effect control surface deployment creating forces to suppress the natural mode induced vibrations on multiple geometric axis&#39;s. More particularly, symmetric and anti-symmetric control surface deployments are used on one or more geometric axis&#39;s to damp lateral, longitudinal, vertical and most importantly torsional vibrational modes.

BACKGROUND OF THE INVENTION

The present invention is directed to the aircraft flight control artand, in particular, to an active control system for suppressing aircraftbody vibrations due to natural mode excitations on multiple geometricaxis.

Generally speaking, the total motion of an airplane is understood bythose in the art, as comprising; 1) rigid body motion and 2) flexiblemotion. The rigid body of airplane includes translation and rotationabout each of the airplane axis. The flexible motion includes verticalbending of fuselage or wings, lateral bending of fuselage or empenage,and torsional motion of fuselage or wings. As airplanes become lighter,larger and longer, the effects of airplane flexibility on passengercomfort and handling quality becomes more critical and attracts higherattention. Large aircraft, particularly those whose fuselage bodies havea high length to diameter ratio, are subject to gust-induced excitationof natural modes of the aircraft body. These modes include naturalbending and twisting of the body in the fore and aft sections of theaircraft. These natural mode excitations are objectionable in commercialaircraft since they can result in passenger and crew ride discomfort orincrease in structural load. However, in some severe cases, the pilotsmight misjudge the vibrations as a limit cycle caused by controloscillatory failure and perform unnecessary corrective actions. Further,when the flight deck pilot station has a lot of vibration, the pilot mayunintentionally couple with the aircraft's motion, thereby involuntarilyputting in control inputs to sustain or amplify the vibrations to higherlevels. This phenomenon is known in the art as “Pilot InducedOscillation” or “Aircraft-Pilot Coupling” or “Aircraft-Pilot AdverseCoupling”.

Most modem commercial aircraft flight control systems have either apassive or active modal suppression systems. Passive systems haveevolved from the earliest designs and are still used, in the interest ofeconomy and simplicity, and usually when the aircraft's vibration levelis low such that a more sophisticated approach is not warranted. Thesesystems were typified by their use of control path notch filters toavoid control signal commands at the aircraft structures—structural modefrequency (natural resonance frequency). However, aircrafts having amore complex structural vibration problem typically require the moresophisticated active systems. These systems sense and process feedbacksignals from appropriate aircraft body locations and move the controlsurfaces to generate forces that reduce such vibration levels. Mostpassive and active modal suppression systems, up until now, reducestructural vibrations in a single geometric axis for its fundamentalharmonic mode, first body bending mode for example.

Many prior passive and active systems have addressed a variety ofaircraft structural modal suppression problems:

(U.S. Pat. No. 2,718,365 White “Deformation Compensator for AircraftControls”) A means to increase the effectiveness of the horizontal tailon the longitudinal axis in the presence of fuselage bending;

(U.S. Pat. No. 2,832,551 Gille “Automatic Pilot for Aircraft”) A systemfor damping lateral fuselage accelerations using rudder deflections;

(U.S. Pat. No. 2,985,409 Atwood et al. “Gust Alleviation System”) Asystem for “canceling or diminishing the unpleasant effects onpassengers” of gust induced vertical accelerations;

(U.S. Pat. No. 3,079,108 Falkner et al. “Control Apparatus”)A system forsuppressing aircraft fuselage body bending modes;

(U.S. Pat. No. 3,240,447 Olshausen “Vehicle Control System”) Alongitudinal gust alleviation system that uses canards to producecompensatory changes in lift without affecting the crafts pitchingmoment

(U.S. Pat. No. 3,241,077 Smyth et al. “Self-Adaptive Control SystemEliminating Variable Unwanted Component”) A variable notch filter usedfor decoupling resonant loads from the control system over broad dynamicrange;

(U.S. Pat. No. 3,279,725 Andrew et al. “Flight Controller for FlexibleVehicles”) Two actuators, mutually arranged for providing pitchingmoments of opposite sense, to reduce longitudinal body bending inflexible aircraft;

(U.S. Pat. No. 3,347,498 Priestly et al. “Aircraft Structural StressAlleviators”) Wing control surfaces to reduce wing structure fatiguecaused by wing root body bending;

(U.S. Pat. No. 3,636,324 Dommasch “Air Data Lateral-DirectionalStability Augmentation System”) A lateral—directional control system forsuppressing lateral axis body bending, that does not use prior inertialsensors.

(U.S. Pat. No. 3,734,432 Low “Suppression of Flutter”) An active controlsystem for suppression of flutter that includes controlling thetorsional bending of airfoils. Torsion & bending motions and deflectionsare sensed and converted by a stability control augmentation system intoleading and trailing edge control surface deflections in efforts tocounteract said motions & deflections.

(U.S. Pat. No. 3,902,686 Wykes et al. “Combined Vertical and LateralIdentical Location of Accelerometer and Force System”) Lateralaccelerometers and control vanes are used to reduce the lateral andvertical vibration at the pilots station.

(U.S. Pat. No. 4,455,004 Whitaker “Flight Control Device for Airplanes”)Wingtip mounted control surfaces provide wing load alleviation duringmaneuvering & high speed gusts.

(U.S. Pat. No. 4,706,902 Destuynder et al. “Active Method andInstallation for the Reduction of Buffeting of the Wings of anAircraft”) Wing buffeting alleviation system that applies to wing modeflutter control.

(U.S. Pat. No. 4,796,192 Lewis “Maneuver Load Alleviation system”) Wingload alleviation system that selectively deflects aerodynamic surfacesin response to a real-time structural wing load calculation for thepurposes of moving the wing lift vector inboard thereby reducing themoment arm by which it is acting.

(U.S. Pat. No. 4,821,981 Gangsaas et al. “Maneuver Enhancement and GustAlleviation System) A maneuver enhancement & gust load alleviationsystem that coordinates the control & effects of multiple aircraftcontrol surfaces that are otherwise adversely coupled.

(U.S. Pat. No. 5,186,416 Fabre et al. “System for Reducing the ForcesApplied to the Wings and Particularly to the Root of the Wings of anAircraft in Flight”) Wing load alleviation system that deflectsaerodynamic surfaces in response to sensed vertical accelerations forthe purposes of reducing wing root bending moments.

(U.S. Pat. No. 5,072,893 Chakravarty et al. “Aircraft Modal SuppressionSystem”) An accelerator & rudder based suppression system to damp aftbody lateral accelerations after they occur for the purposes ofimproving ride quality.

(U.S. Pat. No. 5,224,667 Lacabanne “System Enabling the Flutter Behaviorof an Aircraft to be Improved”) An accelerometer and rudder basedcontrol system for suppressing lateral bending modes.

(U.S. Pat. No. 5,375,794 Bleeg “Apparatus and Method for ReducingAircraft Loads Resulting from Atmospheric Turbulence and Gusts”)Pressure sensor & rudder based gust load alleviation system thatsuppresses weather-vane (beta) rotational modes for the purposes ofimproving ride quality.

(U.S. Pat. No. 5,452,865 Tran et al. “Aircraft Frequency Adaptive ModalSuppression System”) Modal suppression system that uses dynamic fuelparameter to modify modal suppression control law.

(U.S. Pat. No. 5,598,991 Nadkarni et al. “Method and Apparatus forDetecting Oscillatory Phenomena Indicative of Airflow Separation”) Flowseparation monitor improvement to differential pressure sensor basedU.S. Pat. No. 5,375,794.

(U.S. Pat. No. 5,667,166 Tran et al. “Aircraft Frequency Adaptive ModalSuppression System”) Modal suppression system that uses gross weight tomodify modal suppression control law.

(U.S. Pat. No. 5,669,582 Bryant et al. “Method and Apparatus forReducing Unwanted Sideways Motion in the Aft Cabin and Roll-Yaw Upsetsof an Airplane due to Atmospheric Turbulence and Wind Gusts”)Improvements to U.S. Pat. No. 5,375,794.

(U.S. Pat. No. 5,833,173 Tran et al. “Aircraft Frequency Adaptive ModalSuppression System”) Improvement to U.S. Pat. No. 5,072,893.

From the foregoing discussion, it is well settled in the art to usefilters to suppress structural resonance exciting command inputs.Further, it is settled in the art to sense bending & torsional momentsof structures caused by gusts, high maneuvering load factors andstructural resonances, and to alleviate these upsets through the use ofa stability augmentation computer, usually with sensors and flightcontrol effectors in the vicinity of the upset. Moreover, the prior arthas been concerned with applications of axis-symmetric flight controlinputs, on a particular control axis to counteract a structural upset onthe same axis. However, what is not known, concerns the use ofanti-symmetric control inputs on one control axis to counteract theeffects of control inputs or structural resonances on another controlaxis.

For these reasons, there is a need for a comprehensive strategy toaddress structural modal suppression on multiple geometric axis's.Further, there is a need for a simultaneous multi-axis flight controlsystem apparatus wherein all axis flight controls are utilized toalleviate structural resonances of airfoil, aircraft body bending andtorsional moments. Still further, there is a need for an active modalsuppression control system that is capable of accurately monitoringaircraft structural vibrations due to excitation of natural aircraftbending and torsional modes, wherein the airplane's control surfaces aremoved in such a way as to reduce the flexible motion at the same timecontrolling the rigid body motion.

BRIEF SUMMARY OF THE INVENTION

The present invention, therefore, is directed to an active aircraftmodal suppression system that is capable of accurately sensing modalinduced oscillations and producing control signals to deploy controlsurfaces to suppress such oscillations.

According to the invention, an aircraft multi-axis modal suppressioncontrol system suppresses aircraft body deflections due to natural bodyflexible modes and comprises control surface means which is controllablydeployable in response to input control signals. Accelerometers, rategyros, and/or pressure ports are predeterminedly located on the aircraftbody to sense signals that are representative of the predeterminednatural modes. In a particular implementation of the invention, the mostsignificant and objectionable body bending modes and the torsional modesare suppressed. Also, conventional means are employed to produce avelocity signal representative of aircraft velocity. The controlalgorithm is responsive to the pressure ports, sensed accelerations,and/or attitude rates, and the aircraft velocity signal such that thecontrol surfaces are deployed to create forces on the aircraft body tosuppress the natural mode induced oscillations at different flightphases.

In a further aspect of the invention, a conventional altitude meansproduces an altitude signal representative of aircraft altitude and thecontrol algorithm includes means responsive to the altitude signal forproducing the control surface control signals.

In yet a further aspect of the invention, the signals produced by thepredeterminedly located sensors are processed through frequencysensitive modal filters such that the desired modal control signals aregenerated at the proper phase to suppress the structural vibrationsrather than exciting them.

In the lateral axis, besides the conventional usage of rudder to controlthe lateral body bending mode, one aspect of this invention is to useanti-symmetric elevator control surface deflections or positions tocontrol body torsional mode.

In yet another aspect of the invention, anti-symmetric flaperon controlsurface deflections or positions are used to control wing torsional modeand body tortional mode.

In the longitudinal axis, in addition to the usage of symmetric elevatorto control the vertical body bending mode, a further aspect of thisinvention is to use symmetric flaperon control surface deflections orpositions to control vertical wing mode.

It is understood by those skilled in the art that a sufficient number ofsensors other than what is currently shown in the preferred embodimentscan be employed to provide information needed to suppress the structuralmodes. It is further understood that different control effectors otherthan what currently shown in these embodiments can also be deployed toprovide the necessary modal damping, without departing from the spiritof the present invention. For example, as shown in FIGS. 7 a & 7 b, a“canard configured” aircraft would utilize canard control surfacedeflections in conjunction with wing and/or tail control surfacedeflections, within the scope and teaching of the present invention.

In the preferred embodiment of the present invention, the multi-axismodal suppression control law is implemented wherein the rigid bodycontrols are augmented by a functionally separated novel modalsuppression control system. However, in an alternate control systemembodiment, the rigid body control are designed in an integrated fashionwith the novel modal suppression system herein called the IntegratedMulti-Axis Modal Suppression System.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 shows a conventional aircraft configuration having an arrangementof input sensors as disposed within an aircraft in accordance with thepreferred embodiment of the present invention that includes: inertialreference units, air data computer, accelerometers at the aft andforward body locations, and wing box front spar mounted rate gyro andaccelerometers.

FIG. 2 shows a block diagram of the preferred embodiment of themulti-axis modal suppression control law in which the rigid body controllaws are integrated functionally independent of the modal suppressionsystem.

FIG. 2 a shows the Roll Stability Augmentation Control Algorithm used inaccordance with the preferred embodiment of the Multi-Axis ModalSuppression System.

FIG. 2 b shows the Yaw Stability Augmentation Control Algorithm used inaccordance with the preferred embodiment of the Multi-Axis ModalSuppression System.

FIG. 2 c shows the Pitch Stability Augmentation Control Algorithm usedin accordance with the preferred embodiment of the Multi-Axis ModalSuppression System.

FIG. 3 is a power spectral density graph illustrating the improvement tothe torsional vibrational airplane body mode response using when therudder and anti-symmetric elevator are used as control effectors actingin response to an anti-symmetric elevator servo input excitation source.

FIG. 4 is a power spectral density graph illustrating the improvement tothe lateral body bending mode response when the rudder andanti-symmetric elevator are used as control effectors acting in responseto a rudder servo input excitation source.

FIG. 5 is a power spectral density graph illustrating the improvement tothe vertical body bending mode response when symmetric elevators areused as the main control effectors acting in response to a symmetricelevator servo input excitation source.

FIGS. 6 a and 6 b show multiple view of a conventional aircraftconfiguration having a arrangement of possible input sensors as disposedwithin a aircraft: IRU, ADC, rate gyros, and accelerometers at the aftand fwd bodies location, rate gyros & accelerometers at the wing boxfront spa, and rate gyros, accelerometers at the empenage.

FIGS. 7 a & 7 b show multiple views of a non-conventional canardconfigured aircraft having an arrangement of possible input sensors asdisposed within an aircraft in accordance with the present inventionthat includes: inertial reference units, air data computer,accelerometers at the aft and forward body locations, and wing box frontspar mounted rate gyro and accelerometers.

FIG. 8 is a table that summarizes the novel control algorithm's transferfunction wherein control inputs solutions are suggested for thesuppression of lateral, vertical, or torsional modal accelerations orvibrations on all geometric axes.

FIG. 9 is a block diagram of the embodiment of the Integrated Multi-AxisModal Suppression control law wherein the rigid body control laws aredesigned in an integrated fashion with the modal suppression system.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates the side view of a conventional commercial aircraft.The problem exhibited by such aircraft to which the present invention isaddressed is that the flexible structure is subject to vibrationsresulting from external forces, such as gusts or pilot control inputs,exciting natural resonant modes of the body. Of particular concern dueto passenger discomfort are the body bending vibrations and bodytwisting torsional modes.

The present invention is an active system for suppressing the bodybending modes and the torsional modes.

FIG. 1 depicts the sensors required to feed into the control lawalgorithm of the preferred embodiment of the multi-axis modalsuppression system as shown in FIGS. 2, 2 a, 2 b & 2 c. The feedbacksensors include an inertial reference unit 60 a (hereinafter IRU)located at the Electronics Equipment (hereinafter EE) Bay 52 at thefront belly of the aircraft 50; along with the IRU 60 a, an air datacomputer 60 b (hereinafter ADC) is also required; a pitch rate gyro 61located in the vicinity of the wing box front spar 50 c is also used inthe present invention; finally, dedicated forward accelerometers 62 aand aft galley accelerometers 62 b at the forward 50 a and aft 50 bairplane body locations, respectively, are also deployed. In general,the wing box front spar pitch rate gyro 61 and the IRU sensors 60 atogether provide the attitude and acceleration signals for the rigidbody mode stability augmentation. The ADC 60 b provides the speed and/ordynamic pressure for control law gain scheduling such that proper amountof surface deflection can be applied at different speed/dynamic pressureconditions even though similar vibration levels are sensed. For modalsuppression, the dedicated accelerometers 62 a, 62 b and the IRU rategyro and accelerometer sensors usually provide the necessary structuralmode contents. It is understood that the location of the EE Bay 52 hasbeen a matter of historical convention wherein all electronics weresituated in the vicinity of the flight deck. However, other locations ofthe EE Bay will not depart from the spirit of this invention. Further,it is also understood that the modern trend towards integrating amultiplicity of systems, such as the integration of the IRU 60 a & theADC 60 b into the Air Data Inertial Reference Unit (hereinafter ADIRU)will similarly not depart from the spirit of the present invention.

This feedback sensor embodiment according to the present inventiondiffers from conventional designs with the addition of the pitch rategyro 61 in the vicinity of the wing box front spar 50 c. It has beenfound, that wing box sensors are preferred and have an advantage overthe IRU signals for rigid body controls due to the lack of structuralmode contents at the wing box front spar area, thereby reducing anyinadvertent coupling of the structural mode excitation. This phenomenonis simply an exploitation of the relatively stiff structures thatcharacterize the wing box vicinity. Although the preferred embodiment ofthe present invention only utilizes a pitch rate gyro 61 in the vicinityof the wing box front spar location 50 c, other dedicated gyros andaccelerometers can also be deployed at this location and its vicinities,if necessary, to minimize any rigid body/structural mode couplings.

FIG. 2 depicts the control law algorithm of the present multi-axis modalsuppression system preferred embodiment. It contains of a Roll StabilityAugmentation System (hereinafter SAS) 21, a Torsional Wing Mode ControlAlgorithm 22, a Yaw SAS 23, a Fore Body Lateral Bending ControlAlgorithm 24, an Aft Body Lateral Bending Control Algorithm 25, aTorsional Body Mode Control Algorithm 26, a Vertical Wing Mode ControlAlgorithm 27, a Vertical Body Bending Mode Control Algorithm 28, and aPitch SAS 29. Each of these control algorithms will be explained furtherin the following discussion.

The Roll SAS 21 is shown in FIG. 2 a. The Roll SAS uses the IRU rollattitude signal 3 to provide rigid body roll attitude control. Loopdamping is provided by IRU roll attitude rate signal 2. Wheel force 1 isused to determine when to activate the roll attitude control. Roll notchfilters 41 at different structural mode frequencies are generally usedto desensitize the roll flaperon command 30 from exciting any structuralmodes. The roll flaperon command controls the left and the rightflaperons in opposite direction but with the same amplitude. Hereafter,a command that causes the motion of the control surfaces to move inopposite direction but with the same amplitude will be referred to asanti-symmetric command. The ADC calibrated airspeed 18 is used for gainscheduling 41 a.

The Torsional Wing Mode Control Algorithm 22 uses the IRU body roll rate4 to provide “wing torsion” structural information so that ananti-symmetric flaperon command 31 may be generated to control thismode. The torsional wing modal suppression filter 22 is designed toprovide the proper gain and phase relationship such that anti-symmetricflaperon would be deployed at the right moment with the right amplitude.Calibrated airspeed 18 is used for gain scheduling, It is understood bythose skilled in the art that the sensor placement, the use of othersensors, or use of other control effectors may be used, if found to bemore efficient, without departing from the spirit of the presentinvention.

FIG. 2 b shows the Yaw SAS 23. The primary function of the Yaw SAS 23 isto generate a rudder command for rigid body dutch roll damping andcoordinated turn entry/exit, damping and to allow the airplane tosustain a constant steady state turn. The feedback sensors include: IRUbody yaw rate 8, IRU body roll rate 4, IRU roll attitude 3, and IRUlateral acceleration 9. In addition, body angle of attack 5 and trueairspeed from the ADC 6 are also fedback. These signals form asynthesized sideslip rate signal 42 to provide dutch roll damping andturn entry/exit coordination. Dynamic pressure 18 a from the ADC is usedfor gain scheduling 43. The signal is then passed through a series ofyaw notch filters 44. Steady state turn coordination guidance, isprovided by passing the yaw turn signal 45 through a gain scheduler 46,which in turn is a function of calibrated airspeed 18 and flap position7. Finally the yaw damper rudder command 32 is produced.

Dedicated accelerometers (62 a, 62 b) in FIGS. 6 a & 7 a at the pilotstation 50 a and at the aft galley 50 b are used as the main feedbacksensors for the fore and aft lateral body bending control (24, 25)inFIG. 2 respectively. Each sensor passes through its own modalsuppression algorithms, the Fore Body Lateral Control Algorithm 24 andthe Aft Body Lateral Control Algorithm 25 respectively, before they aresummed to form a modal rudder command 33. Again, calibrated airspeed 18is used for gain scheduling.

The Torsional Body Mode Control Algorithm 26 uses the IRU lateralacceleration 9 to provide “body torsion” structural information so thatan anti-symmetric elevator command 34 may be generated to control thismode. The torsional body modal suppression filter 26 is designed toprovide the proper gain and phase relationship such that anti-symmetricelevator would be deployed at the right moment with the right amplitude.Calibrated airspeed 18 is used for gain scheduling.

The Vertical Wing Mode Control Algorithm 27 uses the IRU body pitch rate12 to provide “symmetric wing bending” structural information so that asymmetric flaperon command 35 may be generated to control this mode. Thevertical wing modal suppression filter 27 is designed to provide theproper gain and phase relationship such that symmetric flaperon would bedeployed at the right moment with the right amplitude. Calibratedairspeed 18 is used for gain scheduling.

The Vertical Body Mode Control Algorithm uses the IRU normalacceleration 13 to provide “fore body vertical bending” structuralinformation so that a symmetric elevator command 36 may be generated tocontrol this mode. The vertical body modal suppression filter 28 isdesigned to provide the proper gain and phase relationship such thatsymmetric elevator would be deployed at the right moment with the rightamplitude. Calibrated airspeed 18 is used for gain scheduling.

FIG. 2 c shows the Pitch SAS 29. The Pitch SAS is a full timeaugmentation system that provides rigid body pitch axis stability foraircraft control systems that have been built with relaxed-staticstability. In addition to pitch damping, the system also can provide C*controls, pitch attitude control, stall and overspeed protection, andlong term speed control. The wingbox front spa pitch rate sensor 14located in the vicinity of the wing box front spar 50 c (FIGS. 6 a & 7a) is used instead of IRU body pitch rate 12 (FIG. 2), to minimizestructural coupling. IRU normal accelerometer 13, IRU pitch attitude 15,IRU flight path acceleration 16, Flight Management Control System speedlimits 19, and Autopilot Mode Control Panel selected speed 20 are alsoused as feedback sensors. Column Force 17 is used to determine when toactivate pitch attitude control. Pitch notch filters 49 at differentstructural mode frequencies are used to desensitize the pitch elevatorcommand 37 from exciting any structural modes. The ADC dynamic pressure18 a & calibrated airspeed 18 are also used for gain scheduling 47 & 48

The roll flaperon command 30 in FIG. 2 is then summed with theanti-symmetric flaperon command 31 and the symmetric flaperon command 35to form the flaperon command 38.

The yaw damper rudder command 32 is then summed with the modal ruddercommand 33 to form the rudder command 39.

The anti-symmetric elevator command 34 is then summed with the symmetricelevator command 36 and the pitch elevator command 37 to form theelevator command 40.

FIGS. 3, 4 and 5 show the Power Spectral Density plots of various modesrecorded by different sensors to demonstrate the effectiveness of thepresent invention.

FIG. 3 illustrates the improvement to the torsional airplane body moderesponse when the rudder and anti-symmetric elevator are used as controleffectors acting in response to an anti-symmetric elevator servo inputexcitation source.

FIG. 4 illustrates the improvement to the lateral body bending moderesponse when the rudder and anti-symmetric elevator are used as controleffectors acting in response to a rudder servo input excitation source.

FIG. 5 illustrates the improvement to the vertical body bending moderesponse when symmetric elevators are used as the main control effectorsacting in response to a symmetric elevator servo input excitationsource.

FIGS. 6 a and 6 b show multiple views of a conventional aircraft withpossible sensor locations to be used in a multi-axis modal suppressionsystem. It shall be understood that not all the sensors presented in thefigures are necessary but rather to show a variety of sensors that canbe used for the design. For example, if desired to have less couplingwith the structural modes, the rigid body stability augmentation systemcould utilize more of the sensors located at the wing box rather thanthose from the ADIRU. Similarly, pressure port may be favor forcontrolling structural mode over accelerometers or gyros.

FIGS. 7 a and 7 b show multiple views of a non-conventional canardconfigured aircraft with possible sensor locations to be used in amulti-axis modal suppression system. Sensors can be installed on thecanard surfaces if found to be more advantageous.

The preferred multi-axis modal suppression system shown in FIG. 2 uses adedicated control effector for each particular structural mode. However,as demonstrated in FIGS. 3 through 5, any one control surface cancontrol, and hence excite, different structural modes. FIG. 8 shows atable that summarizes the type of vibrational motion and an appropriatecontrol surface application to suppress thereof.

FIG. 8 provides a summary of vibrational mode problems and control inputsolutions in accordance with the systematic method and apparatus of thepresent invention. The table illustrates that any given control surfacecan affect more than one type of vibrational motion. Furthermore, it isunderstood that each type of vibrational mode includes many modes ofvibration, known in the art as harmonics, and that control surfaces arechosen to control these various modes as well. Ideally, it is desired tohave just one control surface to control all the structural modes,nevertheless it is known to those skilled in the art that this designapproach is hard to achieve and hence usually require the use ofmultiple control surfaces to control the different structural modes. Forexample, the rudder surface may be selected to provide damping for thelateral body bending mode and also the torsional body-bending mode,while the torsional wing mode is left for the anti-symmetric flaperon tocontrol. The appropriate selection of modes to be damped by each surfaceis determined by engineering judgment and optimized use of the surfacedetermined by the effectiveness of the surface on the particular modeand the robustness of the resultant control law. Ideally, the designchoice will depend on a parametric analysis of both technical andeconomic data. A technical concern may consider whether any surfaces maybe working against other surfaces, a phenomenon known in the art as“adverse coupling”. Another technical concern is whether the use ofparticular surfaces to solve vibrational problems may use up reservecontrol authority, a phenomenon known as “control saturation”. Economicconsiderations may mitigate against a particular surface utilization inconsideration of maintenance impacts and part life cycle reduction.

It is known that one control surface can be used to remove undesirableeffect of another control surfaces. For example, if the rudder is usedto damp the lateral bending mode at a particular frequency, however itsdedicated sensors at times could also pick up signals of otherstructural modes at other frequencies. As a result, the motion of therudder may further exasperate the existing torsional body mode. In thiscase, anti symmetric elevator may be commended to generate at theappropriate frequency to negate the torsional effect of the rudder.Similarly, one may choose the anti-symmetric flaperon to negate thetorsional effect of rudder. To provide such a cross-feed, it isunderstood in the art that appropriate filtering design is required.This approach is known in the art as control harmonization. Thus thereis a need to design a modal suppression system in an integrated way suchthat when the modal command of one control axis is controlling itsprincipal structural mode, the present modal command is cross-fed to theother control axis to make sure its effect on other structural modescould be negated by the inputs of the other control surfaces.

FIG. 9 depicts an Integrated Multi-Axis Modal Suppression System whereinthe rigid body controls are designed in an integrated fashion with thenovel modal suppression system, as distinguished from the preferredembodiment of the present invention's functionally separated,“augmented” approach.

Control law sensor inputs for this integrated modal suppression systemis similar to the preferred embodiment of the Multi-Axis ModalSuppression System. They include: vertical acceleration; lateralacceleration; attitude; altitude rate and acceleration; and pressuredistribution on the surfaces. These sensors are distributed along thebody of the airplane or on the control surfaces. It is understood thataltitude and altitude rate; air data; airplane weight and inertia areused by designers to provide appropriate gain scheduling.

The Roll, Yaw and Pitch Stability Augmentation Systems (for rigid bodymode enhancement) of the preferred embodiment of multi-axis modalsuppression system, as shown in FIG. 2, are designed independent of themodal suppression system. They are generally supplemented withstructural notch filters to minimize any structural couplings. However,today's computer-aid design environment when powerful software programscan design multiple loop control algorithm simultaneously. Somedesigners may choose This Integrated Multi-Axis Modal Suppression Systemdesign is to design both the rigid body stability augmentation controllaws and the modal suppression systems in an integrated fashion suchthat the stability augmentation commands, besides controlling the rigidbody modes, may also be allowed to pass through some structural modefrequencies to assist in damping out the corresponding structural modes.One advantage of this particular approach is that it may not benecessary to include any notch filters in its stability augmentationcontrol laws. This concept is demonstrated in FIG. 9 with the modalfilters shown adjacent to each of the stability augmentation system.

1. A system for controlling deformation of an aircraft during flight,comprising: a receiver coupled to at least one aircraft sensor toreceive an input indicative of excitation of a torsional mode of a bodyof an aircraft about a longitudinal axis of the aircraft during flight;and a processor coupled to the receiver, the processor being furthercoupled to a first elevator surface on a first side of the longitudinalaxis and a second elevator surface on a second side of the longitudinalaxis, the processor being configured to: direct a first output signal tothe first elevator surface to deflect the first elevator surface in afirst direction; simultaneously direct a second output signal to thesecond elevator surface to deflect the second elevator surface in asecond direction opposite the first direction to actively counterexcitation of the torsional mode of the body of the aircraft; and whileactively countering excitation of the torsional mode of the body of theaircraft, direct a third output signal to the first and second elevatorsurfaces to move the first and second elevator surfaces in the samedirection to control a pitch attitude of the aircraft.
 2. The system ofclaim 1, further comprising the aircraft.
 3. The system of claim 1wherein the processor is configured to direct the first and secondelevator surfaces to move at a first frequency to at least partiallycounter the force applied to the aircraft and simultaneously control aflight attitude of the aircraft by directing the first and secondelevator surfaces to move at a second frequency less than the firstfrequency, with the first and second frequencies of motion superimposed.4. A system for controlling deformation of an aircraft during flight,comprising: a receiver coupled to at least one aircraft sensor toreceive an input indicative of excitation of a torsional mode of a bodyof an aircraft about a longitudinal axis of the aircraft during flight;and a processor coupled to the receiver, the processor being furthercoupled to a first control surface on a first side of the longitudinalaxis and a second control surface on a second side of the longitudinalaxis, the processor being configured to: direct a first output signal tothe first control surface to deflect the first control surface in afirst direction; simultaneously direct a second output signal to thesecond control surface to deflect the second control surface in a seconddirection opposite the first direction to actively counter theexcitation of the torsional mode of the body of the aircraft; and whileactively countering the excitation of the torsional mode of the body ofthe aircraft, direct a third output signal to the first and secondcontrol surfaces to move the first and second control surfaces in thesame direction.
 5. The system of claim 4 wherein the processor isconfigured to direct the first and second control surfaces to move at afirst frequency to at least partially excitation of the torsional modeof the body of the aircraft and simultaneously control a flight attitudeof the aircraft by directing the first and second control surfaces tomove at a second frequency less than the first frequency, with the firstand second frequencies of motion superimposed.
 6. The system of claim 4wherein the first control surface includes a first elevator on a firstside of a longitudinal axis of the aircraft, and wherein the secondcontrol surface includes a second elevator on a second side of thelongitudinal axis of the aircraft.
 7. The system of claim 4, wherein theat least one sensor includes a pitch rate sensor positioned at leastproximate to a wing body junction of the aircraft.
 8. The system ofclaim 4, wherein the at least one sensor includes a pitch rate sensorpositioned at a forward spar of a wing box of the aircraft.
 9. A systemfor controlling deformation of an aircraft during flight, comprising: areceiver configured to receive an input corresponding to at least oneforce applied to an aircraft during flight; a processor coupled to thereceiver and to right and left elevators of the aircraft, the processorbeing configured to: direct the left and right elevator surfaces to movesymmetrically to control a pitch attitude of the aircraft;simultaneously direct the left and right elevators to move symmetricallyto actively control bending of a fuselage of the aircraft; andsimultaneously direct the left and right elevators to moveantisymmetrically actively to control torsion of the fuselage of theaircraft.
 10. The system of claim 9, further comprising the aircraft.11. The system of claim 9, further comprising at least one sensorcoupled to the receiver to transmit the input.